The present invention relates to an optical transmitter, for instance, used for communication using an optical fiber. More particularly, the invention relates to an optical transmitter for implementing a screening test of a light-emitting diode.
A light-emitting diode is generally used in various kinds of electronic equipment including an optical transmitter causing a light signal to be incident into an optical fiber. In particular, the reliability of the light-emitting diode used for the optical transmitter is important.
In general, a semiconductor element such as a light-emitting diode and so forth initially incorporates inferior goods with prescribed probability. Thus, such inferior goods are removed in the process of the selection (screening) after manufacturing. In this screening process, the elements to be screened are mounted on a heat sink and so forth, or are assembled in a module. The screening process causes the element to be screened under conditions more severe than those of normal use. Large and small changes in the characteristics of the element are checked before and after screening under the severe conditions. When the change in the characteristics is larger than the prescribed change, the element is removed as inferior goods.
Now, in general, when the process causes a light-emitting diode to be selected before being arranged on an optical transmitter, the light-emitting diode is selected as being a single element. In order to select the light-emitting diode as being the single element, for instance, as shown in the Japanese Patent Application Laid-Open No. HEI 10-160785 which discloses a technique about selection of a semiconductor laser, it is not necessary to measure current-light output characteristics. It may be accomplished by measuring other characteristics such as current-voltage characteristics of the light-emitting diode.
However, in such a method, even though the inferior goods are removed from the light-emitting diode after manufacture, if the process causes the light-emitting diode to be damaged in the assembling stage to the optical transmitter, the inferior goods are mixed with the optical transmitter as being finished goods. Consequently, it is necessary to implement the selection two times, thus the cost becomes high because of the selection process. The technique disclosed in the Japanese Patent Application Laid-Open No. HEI 4-321288 implements the selection of the element under the condition that the drive circuit is connected to the element similar to the semiconductor laser drive circuit. However, in the case of the optical transmitter, such a selection is incapable of being implemented. As is described hereinafter.
FIG. 1 shows a conventional device for selection of the light-emitting diode. The light-emitting diode 12 and the light-emitting diode drive integrated circuit (LD drive LSI) 13 for driving thereof are arranged in the optical transmitter 11. The optical transmitter 11 is provided with two terminals of a power supply terminal for light-emitting diode 14 and a power supply terminal for drive circuit 15. When the process implements selection of the light-emitting diode 12, it is capable of discriminating a change of the characteristic in a short time because the process causes the light-emitting diode to be driven under high temperature. For that reason, the process of the screening is implemented with the condition that the optical transmitter 11 is contained in the isothermal vessel 17. The isothermal vessel 17 is maintained with prescribed temperature while this manufacturing process is implemented by the control circuit 18. Further, the control circuit 18 applies prescribed voltage both to the power supply terminal for light-emitting diode 14 and the power supply terminal for drive circuit 15 from the constant-voltage source 19 while the present manufacturing process is implemented, thus the control is implemented such that the prescribed current 21 flows into the light-emitting diode 12.
In the optical transmitter 11 shown in FIG. 1, the current 21 which flows at the time of the manufacturing process of selection to the light-emitting diode 12 is larger than the ordinary value. However, the present current value is remarkably larger than the current value which the LD drive LSI 13 is capable of driving the light-emitting diode 12. Consequently, it is incapable of implementing the selection of the light-emitting diode 12 while using the LD drive LSI 13 after the LD drive LSI 13 and the light-emitting diode 12 are mixed to be mounted. Of course, it is not economical that the optical transmitter is produced while using together the LD drive LSI 13 capable of driving the light emitting diode 12 with large current and the light-emitting diode 12.
In view of the foregoing, it is an object of the present invention in order to overcome the above-mentioned problems, to provide an optical transmitter which mounts the light-emitting diode and the driving circuit for driving thereof at regular time in mixed condition, and which is capable of selecting the light-emitting diode.
According to a first aspect of the present invention, for achieving the above-mentioned object, there is provided an optical transmitter which includes a light-emitting diode, a drive circuit for outputting a light signal while driving the light-emitting diode which is connected between two electrodes of an anode and a cathode of the light-emitting diode, a voltage applying terminal for light-emitting diode which is arranged on a package on which these light-emitting diode and the drive circuit are mounted, for applying voltage to one electrode of the light-emitting diode, and a current supplying terminal for light-emitting diode selection which is arranged at the package for applying current at the time of screening of the light-emitting diode to the other electrode of the light-emitting diode.
According to a second aspect of the present invention, there is provided an optical transmitter which includes, a light-emitting diode, a drive circuit for outputting a light signal while driving the light-emitting diode which is connected between two electrodes of an anode and a cathode of the light-emitting diode, a voltage applying terminal for light-emitting diode which is arranged on a package on which these light-emitting diode and the drive circuit are mounted, for applying voltage to one electrode of the light-emitting diode, a current supplying terminal for light-emitting diode selection which is arranged at the package for applying current at the time of screening of the light-emitting diode to the other electrode of the light-emitting diode, and a switch for turning ON/OFF electrically between the current supplying terminal for light-emitting diode and another electrode of the light-emitting diode.
According to a third aspect of the present invention, in the first aspect or the second aspect, there is provided an optical transmitter, wherein the current applying terminal for light-emitting diode selection is arranged at rear surface part of the package so as not to protrude to side surface part.
According to a fourth aspect of the present invention, in the first aspect or the second aspect, there is provided an optical transmitter, wherein the one electrode is a cathode, while the other electrode is anode.
According to a fifth aspect of the present invention, in the first aspect or the second aspect, there is provided an optical transmitter, wherein prescribed current which is more than ordinary use is supplied from constant current source with the condition that the package is heated to prescribed temperature in isothermal vessel to the current applying terminal for light emitting diode selection.
According to a sixth aspect of the present invention, in the first aspect or the second aspect, there is provided an optical transmitter, which further includes a constant-current source connected to the current applying terminal for light-emitting diode selection for supplying prescribed current which is more than ordinary use from constant current source with the condition that the package is heated to prescribed temperature in isothermal vessel for the sake of light emitting diode selection, and the control circuit executes temperature control of the isothermal vessel, current control of the constant current source, and an application control of constant-voltage to the voltage application terminal for light-emitting diode.
The above and further objects and novel features of the invention will be more fully understood from the following detailed description when the same is read in connection with the accompanying drawings. It should be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention.
The present disclosure relates to Japanese Patent Application No. 10-232469 filed Aug. 19, 1998, and which is expressly incorporated herein by reference in its entirety.